Evaluation of natural and synthetic photosensitizers in visible light-mediated antimicrobial photodynamic therapy against pathogenic bacteria

Abstract

Antibiotic resistance is the most alarming issue in medicinal treatment against bacterial infections. Alternative effective treatment solutions to antibiotics are long overdue. Long standing antibiotic overuse and unfinished antibiotic courses have become globally life threatening, especially in Bangladesh. An effective alternative way to inactivate pathogenic microorganism is Antimicrobial Photodynamic Treatment (APDT). This study aims to explore the antimicrobial photodynamic activity of hypericin (a naturally occurring nontoxic photosensitizer (PS)) and methylene blue (a chemical photosensitizer), which in combination with light can generate reactive oxygen species (ROS), thus effectively destroying the bacterial cell. Clinically pathogenic bacteria Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 were obtained from a diagnostic laboratory in Dhaka, Bangladesh. Antibiotic susceptibility profiling was performed using the Kirby-Bauer disk diffusion method on Mueller-Hinton Agar (MHA). Overnight bacterial cultures were incubated with the PS, followed by light exposure using an orange LED light. Post-treatment bacterial viability was assessed by enumeration of colony-forming units.PS and light exposure showed successful reduction of S. aureus up to log 3. There was little impact on E. coli, which was utilized in this experiment to represent the reaction of Gram-negative bacteria to APDT. Gram-positive bacteria are more susceptible to antimicrobial photodynamic treatment, as opposed to Gram-negative bacteria. The treat has shown significantly successful results inactivating Gram positive bacteria, but not remarkable for Gram-negative bacteria.